A conventional wide-field optical microscope can capture two-dimensional (2D) images of cross-sections of a sample within the thin focal plane of the objective lens normal to its optical axis. For applications such as imaging cortical neurons of a living brain or studying mechanotransduction and mechanical properties of cells, however, the principle plane of interest is often perpendicular to the cross-sections of the sample captured with the objective lens. Currently, axial plane images (e.g., images of planes parallel to the optical axis of the objective lens) are typically obtained with a confocal microscope by scanning its objective lens, intrinsically limiting temporal resolution. In principle, axial plane images can also be obtained by digital holographic microscopy, but digital holographic microscopy requires coherent light signals and is thus not applicable to incoherent fluorescence signals, critically limiting its applications in biology.